The structure present in URs is not challenging when productive morphophonemic alternations shed light on it, and when there is a clear and systematic phonological condition in the language that justifies the differences between the UR that has to be established and the corresponding surface representation. The challenge, or the uncertainty, appears in those cases in which such morphophonemic alternations do not exist, when they are not fully productive or transparent, and also when alternative interpretations are possible. This is the case of the URs corresponding to words beginning with < esC >- in Catalan (escriure 'to write', estona 'while', espot 'spot'), for which there is a small amount of morphological evidence for treating the initial vowel as underlying or as epenthetic (Wheeler 2005).

The purpose of this paper is twofold. On the empirical side, we aim at contributing to the body of knowledge about the UR of words beginning with < esC >- in Catalan. On the theoretical side, and relying on the empirical results obtained, we provide arguments that support the free-ride approach to morphophonemic learning (McCarthy 2005). On the basis of the casuistry arising from the interaction between word-initial vowel epenthesis in Catalan and particular cases of underapplication of vowel reduction in Majorcan Catalan, we provide empirical arguments, lying inside the grammar, for the underlying absence of the initial vowel in words beginning with < esC >-. On the basis of these results, we show how Majorcan Catalan learners take a 'free ride' in the process of constructing the UR of nonalternating forms by generalizing the pattern -- and the subsequent input-output mapping -- observed in cases with transparent morphophonemic alternations and a parallel syllabification problem.